1. Field of the Invention
The present invention relates to a method and an apparatus for transmitting uplink/downlink data on Time Division Duplexing (TDD) carriers. More particularly, the present invention relates to an apparatus for supporting self-scheduling and cross-carrier scheduling of a User Equipment (UE) on carriers with different TDD configurations so as to transmit acknowledgement channels simultaneously regardless of the scheduled carrier.
2. Description of the Related Art
Long Term Evolution (LTE) is an Orthogonal Frequency Division Multiple Access (OFDMA)-based communication standard designed to support both Frequency Division Duplexing (FDD) and TDD. LTE release 8 has been designed to support FDD and TDD on a single carrier and evolved to LTE release 10 which supports both the FDD and TDD. However, it restricts the TDD operation only to the case where the uplink-downlink configuration should be the same across the carriers. In release 11, the work is expected to continue on supporting TDD operation across the carriers with different uplink-downlink configurations.
Table 1 shows the TDD configurations supported in an LTE Rel. 8 system.
TABLE 1Uplink-downlinkDownlink-to-UplinkSubframe numberconfigurationSwitch-point periodicity012345678905 msDSUUUDSUUU15 msDSUUDDSUUD25 msDSUDDDSUDD310 ms DSUUUDDDDD410 ms DSUUDDDDDD510 ms DSUDDDDDDD65 msDSUUUDSUUD
As shown in Table 1, a total of 7 configurations are supported with 10 subframes in which D denotes a subframe reserved for downlink transmission, S denotes a special subframe capable of supporting both the downlink and the uplink transmission and having a guard period for switching between uplink and downlink transmission, and U denotes a subframe reserved for uplink transmission. Since the TDD configurations differ from each other in position and number of subframes for uplink transmission, the number of Hybrid Automatic Repeat request (HARQ) processes and transmission timings available for UEs vary depending on the TDD configuration. In order to support this, the Physical Downlink Shared Channel (PDSCH)-HARQ-ACKnowledgement (ACK) timing relationship is defined per TDD configuration in downlink transmission, two timings, scheduling-Physical Uplink Shared Channel (PUSCH) timing for scheduling information transmission and PUSCH-HARQ-ACK timing for data transmission and evolved Node B's (eNB's) ACK channel transmission, are defined in uplink transmission.
1) PDSCH to HARQ-ACK Timing
Table 2 shows timing relationships of TDD configurations.
TABLE 2UpLink-DownLink(UL-DL)Subframe nConfiguration01234567890——6—4——6—41——7, 64———7, 64—2——8, 7, 4, 6————8, 7, ——4, 63——7, 6, 116, 55, —————44——12, 8, 7, 116, 5, ——————4, 75——13, 12, 9, 8, 7, 5, 4, ———————11, 66——775——77—
In Table 2, the value 6 for subframe 2 column of configuration 0 indicates that the UE's ACK channel corresponding to the eNB's PDSCH transmission before 6 subframes is transmitted at the 2nd subframe. Table 2 shows the relative time of PDSCH transmission to current uplink ACK channel.
2) Scheduling to PUSCH Timing
Table 3 shows the uplink data channel transmission timing relationship for scheduling of TDD configurations.
TABLE 3TDD UL/DLsubframe number nConfiguration01234567890464616464244344444454677775
Table 3 shows the subframe interval of PUSCH transmitted based on the scheduling control channel received at the nth subframe of downlink transmission. For example, if the uplink control channel is received at the 0th subframe in the configuration 3, this means that the UE transmits uplink data channel after 4 subframes.
3) PUSCH to HARQ-ACK Timing
Table 4 shows the relationship between PUSCH transmission and eNB's ACK channel transmission timings.
TABLE 4TDD UL/DLsubframe number iConfiguration01234567890747414646266366646656664746
Table 4 shows the ACK channel transmission timing to the UE's PUSCH transmission in which, if the eNB has transmitted the ACK channel at the 0th downlink subframe in the configuration 3, this means that the ACK channel is transmitted for the PUSCH transmitted before 6 subframes.
In the downlink HARQ process of an LTE system, which is as asynchronous system, if the erroneous downlink data channel can be retransmitted at a certain timing, erroneous uplink data channel has to be transmitted at a predefined timing in a synchronous manner. This can be a Round Trip Time (RTT) having a value that varies according to the TDD configuration, and if the sum of values at the same position in Tables 3 and 4 is 10, this means that RTT is 10 msec, and otherwise, another RTT can be used. Accordingly, the configurations 1, 2, 3, 4, and 5 are configurations that guarantee the RTT of 10 msec, and the configurations 0 and 6 are the configurations guaranteeing another RTT.
In Release 10, the carrier aggregation technique for using multiple carriers is adopted. Carrier aggregation is a technique in which a UE receives data on multiple carriers. In order to discriminate among carriers, the UE is assigned primary and secondary cells that are referred to as a PCell and an SCell, respectively. The UE can be assigned one downlink and uplink PCell and multiple downlink and uplink SCells. In order to support data communication on multiple carriers, there are two scheduling schemes, i.e., self-scheduling and cross-carrier scheduling.
1) Self Scheduling
The self-scheduling is a method for transmitting, by the eNB, different control channels to the UEs on corresponding carriers. The downlink control channel is transmitted at a control channel region of each carrier separately while the data channel is transmitted through the same carrier on which the data channel has been received. However, the ACK channel of the UE is transmitted only in the PCell to minimize the uplink interference and transmit the ACK channels as multiplexed. In transmitting downlink ACK channel, the ACK channel is transmitted on the carrier where the control channel for downlink scheduling has been transmitted.
2) Cross-Carrier Scheduling
The cross-carrier scheduling is a method for receiving the control channel on a single carrier and for transmitting data channel on multiple carriers. The data channel for scheduling is transmitted through the PCell, and the data channel can be transmitted on all channels while the ACK channels of both the UE and the eNB are transmitted through the PCell.
In Rel. 10, since the carrier aggregation is supported only for the same TDD configuration, the downlink and uplink transmission timings are identical across carriers and if the PCell has uplink and the SCell has uplink and vice versa such that it is possible to support the above-described self-scheduling and cross-carrier scheduling. In the case of aggregating carriers with different TDD configurations, the carrier aggregation can be supported depending on the TDD configurations, the supportability can be determined through super-set/subset relationship.
FIG. 1 illustrates a TDD configuration with a super-set/subset relationship according to the related art, and FIG. 2 illustrates a TDD configuration without a super-set/subset relationship according to the related art.
Referring to FIG. 1, in a case of part 101 and in a case of part 103, there are UL subset and DL subset relationships among the TDD configurations 0, 6, 1, and 2. For example, the configuration 0 is a UL super-set of the configurations 6, 1, and 2, and the configuration 2 is a UL subset and DL super-set of the configurations 1, 6, and 0 simultaneously.
Referring to FIG. 2, In a case of part 201, there are no super-set/subset relationships between TDD configurations 1 and 3. In a case of part 203, there is no super-set/subset relationship between the TDD configurations 2 and 4. In addition, in a case of part 205, there is no super-set/subset relationship between the TDD configurations 3 and 2. For example, these three combinations are not fulfilling both the DL subset and the UL subset.
Such combinations make it possible to determine whether the cross-carrier scheduling and self-scheduling can be supported depending on the type of combination. For example, if the DL of the PCell is the super-set of the SCell, the eNB supports the cross-carrier scheduling in DLs of all the SCells, and if UL super-set is DL at the PCell's UL timing, it is difficult to schedule the corresponding DL subframe. Accordingly, the self-scheduling or the cross-carrier scheduling defined in Rel. 10 can be applied to the cases of using different TDD configurations in Rel. 11 without modification in the following cases.                1) The timing of the PCell follows HARQ process timing of uplink of the PCell regardless of self-scheduling and cross-carrier scheduling.        2) In a case of self-scheduling, the uplink HARQ process timing of the SCell follows the SCell timing regardless of a super-set/subset relationship.        3) In a case of cross-carrier scheduling, the downlink HARQ process timing of the SCell follows the timing of the PCell if the SCell is DL subset of the PCell.        4) In a case of cross-carrier scheduling, the uplink HARQ processing timing of the SCell follows the timing of the PCell if the SCell is the UL subset of the PCell and the UL RTT of the PCell is 10 msec.        
In the above 4 cases, the scheduling can be supported without modification, but for other cases of combinations, modification may be imperative.
Therefore, a need exists for an apparatus for supporting self-scheduling and cross-carrier scheduling of a UE on carriers with different TDD configurations so as to transmit acknowledgement channels simultaneously regardless of the scheduled carrier.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present invention.